Storage systems may utilize an array of random access storage device such as solid-state drives (SSDs, also known as solid-state disks) to provide high performance scale-out storage.
RAID (Redundant Array of Inexpensive/Independent Disks) can provide increased resiliency and reliability to storage arrays. RAID allows reconstruction of failed disks (and parts of disks) through the use of redundancy. RAID 6 defines block-level striping with double distributed parity (N+2) and provides fault tolerance of two disk failures, so that a storage array can continue to operate with up to two failed disks, irrespective of which two disks fail. The double parity provided by RAID 6 also gives time to rebuild the array without the data being at risk if a single additional disk fails before the rebuild is complete. To provide efficient reads, data is stored “in the clear,” whereas parity information can be based on a suitable coding scheme.
U.S. Pat. No. 8,799,705, issued on Aug. 5, 2014, which is hereby incorporated by reference in its entirety, describes a data protection scheme similar to RAID 6, but adapted to take advantage of random access storage.
Existing RAID techniques may be designed to work with an array of disks having equal storage capacity (or “size”). Over time, disk capacities may increase, making it desirable or even necessary to use larger disks when expanding a storage array. Replacing legacy disks with larger disks can be wasteful.